Geoscience Reference
In-Depth Information
O
1
Maximum
O
1
Minimum
12
12
-508
-50
8
18
6
18
6
0
MLT
0
MLT
(a)
(b)
2.2
3
10
5
cm
23
4.1
3
10
4
3.3
3
10
3
27.7
3
10
3
1.2
3
10
2
22.7
3
10
2
No data coverage
2
1.7
3
10
4
24.1
3
10
4
1.4
3
10
3
3.3
3
10
3
2
2.7
3
10
2
21.4
3
10
3
7.7
3
10
3
21.7
3
10
4
Figure 9.8
Examination of the O
+
concentration of the high-latitude winter ionosphere
near 300 km shows two regions of plasma depletions that may result from plasma con-
vection: the midlatitude trough seen near 60
◦
invariant latitude and between 1800 and
2400 h, and the high-latitude hole seen near 80
◦
invariant latitude between 2300 and
0530MLT hours. [From Brinton et al. (1978). Reproduced with permission of the Amer-
ican Geophysical Union.]
persistent feature in the winter, appears sporadically at equinox, and almost
never appears in the summer. This occurrence pattern can easily be attributed to
the movement of the solar terminator, which places this location always in dark-
ness in the winter, partially in darkness at equinox, and completely in sunlight
during the summer. Figure 9.9 summarizes some characteristics of the total ion
concentration and its relationships to a typical high-latitude convection pattern.
9.2.2 Ion Heating Due to Collisions
When ionic and neutral particles collide, the amount of energy exchanged
depends on the relative velocity between the two particles. At high latitudes this
relative velocity can become quite high due to the magnetospheric convection
electric field. Then this energy exchange can significantly affect the ion temper-
ature, the ion composition, and even the neutral wind.
The ion temperature at high latitudes is determined principally by frictional
heating, which occurs whenever a relative velocity exists between the ion and
neutral gases, and by heat exchange with the neutral gas and electron gas. The
former can be described equally well as Joule heating due to the Pedersen current
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